In-situ and meteoric cosmogenic ¹⁰Be constraints on coupling chemical weathering and denudation in monolithologic catchments

Deciphering Earth's surface denudation—encompassing both physical erosion and chemical weathering—is essential for understanding sediment flux and its impact on long-term carbon cycle. However, quantifying denudation and chemical weathering across different timescales remains challenging. Here, we combine the covariation of different fluxes derived from in-situ ¹⁰Be_in (quartz, 250–500 μm), the ratio of meteoric ¹⁰Be_met to mineral-weathered ⁹Be (fine grains, < 63 μm), and water chemistry in granitic catchments from the northeastern China to identify the contribution of chemical weathering to overall denudation. Millennial-scale chemical weathering fluxes (W_bulk) derived from the ¹⁰Be_met/⁹Be ratio in authigenic phase capture signals from both the dissolved phase and the reactive phase (adsorbed onto or precipitated in secondary weathering products), ranging from 7.7 to 12.2 mm/kyr. Modern water chemical weathering fluxes (W_water, 2.1–4.0 mm/kyr), which represent only the dissolved phase flux, are positively correlated with W_bulk (R² = 0.38) but are consistently lower. Assuming constant weathering fluxes over time, this correlation suggests that only one-third of the bulk weathering products are removed through water discharge. The weathering intensity, defined as the ratio of W_bulk to in-situ ¹⁰Be_in denudation flux (D_in), spans a wide range of 0.14–0.39, in contrast to the relatively narrow range of W_bulk. This highlights the dominant influence of physical erosion in these catchments, likely reflecting a “kinetic limitation” on regional silicate chemical weathering. By integrating previously published global data on D_in and W_bulk, we find that W_bulk scales linearly with D_in in log-log space over three orders of magnitude (10–10⁴ t/km²/yr). This relationship contrasts with the relationship between W_water and D_in, which shows highly limited weathering flux in uplands with high D_in. The faster decline of W_water compared to W_bulk as D_in increases suggests that W_water is sensitive not only to D_in but also to water discharge. To expand the application of ¹⁰Be_met/⁹Be to any fine-grain Earth surface sample, unlike the strong dependence of ¹⁰Be_in-derived denudation fluxes on the presence of quartz minerals, we also estimate potential weathering intensity proxies such as the mobilized ⁹Be fraction in dissolved and reactive phases (f_reac^Be9+f_diss^Be9) and the chemical depletion factor (CDF). We find that f_reac^Be9+f_diss^Be9 exhibits a much narrower range (0.22–0.32) compared to W_bulk/D_in. Its insensitivity to weathering intensity is likely due to its strong dependence on particle sorting. Although the CDF is also grain-size dependent and overall higher by 0.29 (< 63 μm) than W_bulk/D_in, we find that the CDF derived from grain sizes of 250–500 μm is roughly consistent with W_bulk/D_in. Therefore, the CDF shows promise as a potential weathering intensity proxy for quantifying catchment-wide denudation fluxes through ¹⁰Be_met/⁹Be-derived chemical weathering fluxes.